MATERIAL HANDLING—TRANSPORTATION OF SOI
Unit rates (assumed):
Craneman..................................... $1.00 per h
Current........................................ 0.05 per k
Net operating cost:
m - (0.5 X 80 X 0.05 + 1.43 X 1 +0.15 X 80) 600 + 0.15 X 10,000 -
C/hour = 0.0896 X 300 = 26.88—say $27 per hour (66)
Miscellaneous Cranes.—Wall and jib cranes, whether stationary or of the traveling type, hoists of various kinds and all other varieties of cranes lend themselves to economic selection and analyses as to probable net cost of operation along lines very similar to those followed in the case of overhead electric cranes. A full knowledge of operating requirements is necessary, suitable provisions should be made for possible expansion, and the mistake avoided of assuming too great a mechanical efficiency for the equipment. An intimate knowledge of costs—labor and equipment—and depreciation expenses is also required for even such approximate estimates, if they are to be at all reliable.
CONVEYORS AND ELEVATORS
Classification.—The classification and terminology for conveying and elevating equipment has grown quite confused and as conveyors are frequently installed at an inclination so that they elevate as well as convey, it is well to classify such material handling equipment as carries a continuous, or approximately so, load under the one head of conveyors and elevators, to distinguish them sharply from other material handling equipment which handle more intermittent loads.
The distinctive merits possessed by conveyors and elevators as thus defined are large hourly capacity, low power consumption and relatively light construction. They are used chiefly to handle loose material in bulk, though special designs are employed for handling material in containers, usually of similar dimensions and weight.
Belt Conveyors.—Endless belts running about end pulleys and supported on the runs by a series of securely mounted idlers, usually of the troughed variety on the conveying run and flat on the return run, though "special purpose" belt conveyors are sometimes furnished with straight, or flat, idlers on the carrying run. The individual pulleys comprising the troughed type of idlers are of uniform diameter so that the peripheral speed of the pulleys at all points of contact with the traveling belt is the same as the belt speed. Troughing idlers may consist of any number of individual pulleys, but an odd number is to be preferred, in order that the center section of the conveying belt may be properly supported (see Fig. 1).
Return idlers, supporting the return run of the belt, are flat, made up of a series of individual pulleys mounted on a common shaft or a single pulley slightly wider than the width of the belt it supports. These return idlers are spaced at about 10 ft. intervals, while the troughing and load-carrying idlers are spaced from 2 to 5 ft. apart, depending upon the width of the belt and the weight of the material handled—the wider the belt, the closer are the idlers spaced. At all loading points, the troughing idlers should be spaced at about two-thirds the spacing required on conveying stretches